Dispensing pipette

ABSTRACT

A pipette is provided with an adjustable dispensing volume and with a control which makes the selected volume effective for repeated dispensing operations or for a one-shot operation. To accomplish this, a glass vial or tube is associated with intake and dispensing valves and a piston is inserted into the tube. The tube is encircled by a sheath connected with the piston and having a flange engaged by an adjustable stop which engages a flange on the sheath and limits the withdrawal of the piston from the tube and hence the fluid intake. It thus limits the amount of fluid dispensed upon the next sequential movement of the piston into the tube. Since the piston moves with the sheath, return movement of the piston to withdrawn position can be prevented by engaging the sheath and this is selectively provided for by a manually controlled pawl which can selectively engage the sheath. The intake and dispensing valves are one-way ball valves. The adjustable stop is specially supported to maintain its accuracy and to prevent it from cocking. Control of the stop is effected by a knob exposed through a casing in which the above-mentioned tube is housed.

United States Patent [191 Croslin [451 Apr. 23, 1974 DISPENSING PIPETTE [76] Inventor: Michael E. Croslin, 41 Wendover Rd., Forest Hills, NY. 11375 [22] Filed: Nov. 17, 1972 [21] Appl. No.: 307,360

[52] US. Cl. 222/32, 23/259, 73/425.4 P,

' 222/309, 222/380, 222/382 [51] Int. Cl B67d 5/26 [58] Field of Search 222/32, 33, 41, 43, 173,

222/189, 309, 378, 340, 380, 382, 386, 387, 388; 128/218 F, 233; 23/259, 292; 116/114; 73/425.4 R, 425.2, 425.4 P; 141/22 Primary ExarriincrRobert B. Reeves Assistant Examiner-Joseph J. Rolla Attorney, Agent, or FirmRoberts & Cohen [5 7 ABSTRACT A pipette is provided with an adjustable dispensing volume and with a control which makes the selected volume effective for repeated dispensing operations or for a one-shot operation. To accomplish this, a glass vial or tube is associated with intake and dispensing valves and a piston is inserted into the tube. The tube is encircled by a sheath connected with the piston and having a flange engaged by an adjustable stop which engages a flange on the sheath and limits the withdrawal of the piston from the tube and hence the fluid intake. It thus limits the amount of fluid dispensed upon the next sequential movement of the piston into the tube. Since the piston moves with the sheath, return movement of the piston to withdrawn position can be prevented by engaging the sheath and this is selectively provided for by a manually controlled pawl which can selectively engage the sheath. The intake and dispensing valves are one-way ball valves. The ad justable stop'is specially supported to maintain its accuracy and to prevent it from cocking. Control of the stop is effected by a knob exposed through a casing in which the above-mentioned tube is housed.

60 19 Claims, 5 Drawing Figures DISPENSING PIPETTE FIELD OF THE INVENTION This invention relates to dispensing devices and, more particularly, to dispensing pipettes for dispensing metered quantities of fluids.

BACKGROUND Devices are known for the dispensing of metered quantities of fluids. One such device is disclosed in US. Pat. No. 3,244,324 which issued to M. Croslin on Apr. 5, 1966. Although this particular device is of unusual efficacy, it is rather large and somewhat expensive to construct.

Other known devices involve electrical components or the like as shown by U.S. Pat. No. 3,665,980 which issued to M. Croslin on May 30, 1972. This latter apparatus is also quite capable but is also large and relatively expensive.

Still other devices lack accuracy and reproducibility of results and are characterized by inferior performance. More over, they do not provide for convenience in mounting or for hand supported or bottle mounted operations. Further, known devices are generally of a construction which leads to larger errors for larger capacities.

In still other devices, problems occur with respect to contamination, auto-claving, adjustability, maintenance, fluid leakage and so forth.

Other patents relating to but different from the invention include US. Pat. Nos. 1,633,293; 3,122,280; 3,166,938; 3,343,539; and 3,646,817.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided a dispensing device which has various modes of operation including repetitive dispensing and one-shot dispensing. The device moreover includes adjustable metering devices consisting, for example, of a cylinder with a piston displaceable therein, the displacement of the piston being controlled by an adjustable stop and a spring which reverses the direction of movement of the piston. The piston is further controlled by the introduction of a device designed to slow the action of the spring loaded piston and to provide that shock will not occur in the liquid to be dispensed. In addition, the arrangement is such as to insure that the chamber will be devoid of air, which in turn guarantees accuracy of the dispensed quantity. The device is further designed to be hand held or reservoir mounted.

it is a general object of the invention to provide improved variable volumetric fluid dispensing apparatus.

Another object of the invention is to provide improved automatic or semi-automatic volumetric pipetting techniques.

Still another object of the invention is to provide improved pipette dispensing capabilities and improved apparatus capable of functioning as a diluter and also capable of dispensing microliter and ultramicroliter quantities of fluid.

Still another object of the invention is to provide dispensing apparatus which offers to the researchers employing Radioimmuno Assay Chromatography a means of obtaining accurate samples in the ultramicroliter range.

It is yet a further object to provide improved dispensing apparatus which provides for a multitude of dispensing capabilities.

Another object of the invention is to provide for a high degree of accuracy and repeatability in dispensing operations.

It is yet another object of the invention to provide mobility for lab use; i.e., such as reservoir mounted or hand-held devices.

Another object of the invention is to provide im proved dispensing apparatus having the capability of dispensing either aqueous or viscous liquids.

Yet another object of the invention is to provide for instant and convenient selection of fluid quantities to be dispensed.

Still a further object of the invention is to provide improved dispensing apparatus adapted for extended use with a minimum of maintenance and capable of maintaining extremely sanitary and antiseptic conditions.

Yet another object of the invention is to provide a volume adjustment operable without the loss of fluids and without spillage and further provided with a unique zero lock-in device.

Still another object of the invention is to provide means for repetitive pipetting with a means for looking out the zero lock-in device.

The pipette of the invention features easy to use push button operation. The unique lock-out device allows for volume change without loss of liquid and/or clumsy handling procedures. The desired quantity is dispensed by a single push on aspring-loaded button, and the pipette reservoir refills itself as the spring-loaded buttonreturns to its original position. This procedure can be used for repetitive pipetting by locking out the zero device. Filling and priming are accomplished in seconds by depressing the plunger and allowing the unit to return to its full position. The unit eliminates fluid shock by the use of a spring-loaded dash pot built into the push button.

The unit of the invention, moreover, can be used as a hand-held or stand mounted pipetter to dispense liquid out of a tip attached to its bottom. In this procedure, nozzles are simply interchanged. Also, valves in the dispenser can be turned around so that liquid flow is reversed. This may be desirable for direct dispensing from a bottle without intermediate tubing connections to a reservoir.

In achieving the above and other objects of the invention, there is provided, generally, a pipette which may be considered as comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and to eject the drawn in fluid via the fluid dispensing means in a dispensing operation. The pipette also includes adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of like amounts of fluid as selected by said adjusting means. Also provided is a further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations.

According to a more specific feature of the invention, the aforesaid control means may include plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation.

According to another feature of the invention, the pipette may comprise a casing into which the aforesaid plunger means is depressible, there being a tube in said casing to receive said plunger means, and support means to support the tube in said casing as well as fixed means to limit the extent to which the plunger means can be depressed relative to said tube. The aforesaid tube is coupled with the intake and dispensing means.

According to another feature of the invention, the aforesaid plunger means may include a sheath encircling said tube and displaceable thereon and piston means in the tube displaceable by or with the sheath.

According to yet another feature of the invention, there may be provided a spring acting on the aforesaid sheath to urge the same to partly withdrawn position relative to the tube.

According to still a further feature of the invention, the aforesaid adjusting means may include an adjustable stop having a position of interference relative to the sheath. The sheath may include a projection to en gage the stop and this projection may be a flange at least partly encircling the sheath.

In accordance with still another feature of the invention, the further means mentioned hereinabove may include a pawl adapted to engage the afore-mentioned projection to hold the piston means in fully depressed position.

According to another aspect of the invention, the afore-mentioned pawl may be pivotally mounted on the casing, there being provided a leaf spring engaging the pawl and moving the same to a position to engage the afore-mentioned projection. In addition, there may be provided a manually operable button to pivot the pawl against the leaf spring to release the projection or to move out of a position of interference with the same. The button, which has been mentioned, is effective to keep the pawl removed from the projection on the afore-mentioned sheath.

A further feature of the invention relates to the fact that the adjustment means may include a threaded rod on which the stop is threadably engaged. Furthermore, there may be provided an index on the stop and a scale on the casing cooperating with the index to show the selected amount of fluid to be drawn in. In addition, and in accordance with a further feature of the invention, there may be provided tie rods parallel to the afore-mentioned threaded rod and passing through the afore-mentioned stop to prevent the latter from cock- According to still another feature of the invention a knob is provided on the aforementioned threaded 'rod to rotate the latter to adjust the above-mentioned stop. The casing will preferably be provided with an opening exposing this know for convenient adjustment.

According to another feature of the invention, the above-mentioned stop may partially encircle the sheath. In addition, there may be provided a means on the above-mentioned fixed means to form a hydraulic seal with the afore-mentioned tube.

According to another aspect of the invention, the above-mentioned piston means includes a rod with a piston being positioned on this rod, there being provided astopper in the afore-mentioned tube, slidably supporting the rod. The stopper may be cup-shaped and there may be provided a cup-shaped hub on the rod with a spring being provided between the hub and stopper.

In accordance with another feature of the invention, the intake and dispensing means may each include a one-way ball valve, these ball valves being reversible in order to reverse the flow of metered fluid through the device. The design of said ball valves includes a particularly advantageous feature of the invention since a part of each ball valve is dimensional and shaped to act as a diaphram, to insure a seal capable of operating at low pressures. The material of these valves is furthermore preferably Teflon.

According to still another aspect of the invention, the intake means may have an external shape adapted to be accommodated in an opening in a reservoir such as a bottle. In addition, there may be provided a filter with a flexible tube coupling the filter to the intake means.

The above and further objects and features as well as the advantages of the invention will be found in the detailed description which follows as illustrated in the accompanying drawing. I

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION As is seen in FIG. 1, the pipette provided in accordance with the preferred embodiment of the invention comprises a casing 10 having thereon a scale 12 with which cooperates an adjustable stop, a portion of which is indicated at 14, having thereon an index 16. The location of the stop is adjustable by means of rotatable knob 18 exposed through an opening 20 in the casing 10. i

The control of the fluid intake and dispensing of metered quantities of fluid is effected through the use of a depressible push button 22, the details of which will be illustrated and discussed hereinafter.

In the illustrated embodiment of the invention, the fluid intake section of the apparatus is shown at 24 and the fluid dispensing part of the apparatus is indicated at 26. In association with the fluid intake part 24 is provided a tube 28 to the bottom of which is force-fit a device 30, in which is located a filter membrane 30(a) held in position by a membrane lock 30(b). The filter serves to filter out impurities in the fluid being dispensed, the device 30 being located in the reservoir or bottle containing the fluid.

It will be noted that the fluid intake part 24 has a frusto-conical surface indicated at 32 and adapted to constitute a stopper or the like which is readily accommo dated in the mouth of a bottle or reservoir so that the entire device can be bottle or reservoir supported.

Also to be noted in FIG. 1 is the pipe 34 which is attached to the fluid dispensing part 26 and through which fluid is dispensed in metered quantities.

By way of example, the tubing 28 may be constituted by Teflon tubing or the like and all of the parts de scribed heretofore may be fabricated of plastic or other such materials which are readily auto-claved or which otherwise are suitable for maintaining sanitary conditions.

In FIG. 2 appears the casing with its opening through which is exposed the rotatable knob 18. In this view, it is seen that the casing 10 has an inverted frustoconical shape and is provided with a relatively thin wall 40 and an opening 42 through which the depressible button 22 passes.

FIG. 2 further illustrates a support member 44 at the bottom of the casing 10 on which are supported a number of other members. One of these members is the fixed member 46. .Other such members are the threaded rod 48 and tie rod 50 as well as tie rods 52 and 54 (FIG. 3).

A glass vial or tube 56 of pyrex or the like is accommodated atop support 44 and is held in position on fixed member 46 by means of a land 58' between grooves 58. Land 58 not only holds the tube 56in position but also forms a hydraulic or fluid seal therewith. Land 58' and grooves 58 cooperate to permit a deformation of land 58' which, being of Teflon or the like, has a plastic memory and thus tends to return to its original shape to form an excellent seal with vial 56 thus constituting a feature of the invention.

It will now be noted that the push button 22 is a hollow sheath which encircles the tube 56 and has a closed end 60 as well as an open end, which is encircled by a flange 62. It will furthermore be noted that the upper end of tube 56 is obturated by a plug or hub 64 which has an upwardly extending flange 66 and is therefore cup-shaped. Moreover, it will be noted that the plug is provided with a central bore 68 through which extends piston rod 70 having a threaded end 72.

On the threaded end of the rod 72 is provided a cupshaped member or stopper 74 having a downwardly extending flange 76. A spring 78 is accommodated between cup-shaped plug 64 and cup-shaped member 74.

The push button 22 or sheath is guided by the casing 10, in part. It is also guided in its movement by an opening provided in collar 86, which is held atop the rods 50, 52 and 54 by means of appropriate screws, one of which is indicated, by way of example, at 88.

Downward movement of the piston rod 70 is controlled by push button 22 due to the closed end 60 thereof abutting against cup-shaped member 74. Upward movement of the rod 70 under the urging of spring 78 is likewise limited by the push button 22, since the push button 22 limits the movement of the rod by containing the cup-shaped member 74. Attached to the bottom of the piston rod 70 is the piston 90. It may be permanently attached to the rod 70 or may be threadably engaged therewith. This piston 90 may be fabricated of plastic and is preferably of a material which is readily auto-claved for purposes of sanitation and the like.

Mounted on the threaded rod 48 is adjustable stop 92, the portion 14 of which is exposed through a window in the casing as has been noted above with respect to FIG. 1. The adjustable stop 92 has an arcuate recess therein and hence partially encircles the sheath constituting the push button 22. The adjustable stop 92 is in a position of interference with the upward movement of the flange 62 on the bottom of the sheath. Hence, adjustment of the position of adjustable stop 92 controls the limit to which the flange 62 can move upwardly and thus limits the extent to which the push button 22 can move upwardly. This, in turn, limits the movement of the piston rod 70 and the piston 90 and therefore limits the fluid intake of the device.

The fluid intake part 24 and the fluid dispensing part 26, each comprise a one-way ball valve as is illustrated in FIG. 5. One given direction of flow through the apparatus is illustrated, by way of example, by arrows 100 and 102 in FIG. 2.

Referring briefly to FIG. 5, it is seen that the one-way valves each comprise a Teflon casing 104 and an obturating plug 106 having a valve seat 108 adapted to accommodate a pyrex glass ball 110, which is springloaded by a 20 percent iridium 80 percent platinum alloy spring 112. The ball is enveloped to about ll3rd of its diameter.

It will be noted that when fluid proceeds through the valve in the direction indicated by arrow 114, the ball 110 will be displaced from seat 108 and fluid will be able to flow out via exit bore 116. If, however, an attempt is made to reverse the direction of flow fluid through the illustrated valve, this will be prevented by I the ball 110 being reseated on the seat 108.

From what has been indicated hereinabove by the description of the structure seen in FIG. 5, it will now be appreciated that fluid drawn into the tube 56 (FIG. 2) will be readily enabled to pass by the one-way valve in fluid intake part 24. However, when the push button 22 is depressed, the fluid drawn into the tube 56 will not be able to escape via the one-way valve in part 24 but will be able to escape through the fluid dispensing part 26, hence, to be discharged through the pipe 34 (FIG. 1

It will also be appreciated that the amount of fluid which is drawn into the tube 56 is controlled by appropriately selecting the position of the adjustable stop 92. This is done by rotation of the knob 18, which rotates the threaded rod 48 and permits the adjustable stop 92 to be threadably adjusted in a vertical sense, such adjustment being indicated by the index 16 (FIG. 1) and its position relative to the scale 12.

From the above, it will also be noted that a depressing of the push button 22 causes a discharge of fluid from the apparatus whereas, a releasing of the push button 22 enables a carefully selected and metered quantity of fluid to be drawn into the device preparatory to the next sequential dispensing operation.

It will also be readily seen that a device is provided which provides a repetitive dispensing operation in sequential dispensing steps in which are dispensed like amounts of carefully metered liquid or fluid. It will be noted that the metering operation takes place independently of the viscosity of the fluid. It will be further noted that a dash pot type of operation results so that no shocks are imparted to the fluid which is especially important when the fluid is susceptible to trauma as, for example, is the case with blood and the like.

The invention, moreover, provides for a one-shot operation in which a single amount of metered fluid is dispensed, whereafter an adjustment can be made of the amount of fluid which is to be dispensed without cumbersome and unwieldy types of operations being involved.

For this purpose, there is pivotally mounted by means ofa pin 120, a pawl 122, the hook of which is indicated at 124. This hook is capable of moving into a position of interference with the upward movement of flange 62. When the pawl 122 and thus the hook 124 is in the illustrated position, the flange 62 will be capable of moving downwardly past the hook 124 but will not be able to escape upwardly past said hook. This will hold the piston 90 in its lowermost position against the fixed member 46 so that additional fluid will not be drawn into the tube 56 after one dispensing operation has been effected by a depressing ofthe push button 22.

A leaf spring 130 is mounted, for example, on the rod 50 by means of bolts 132 and rests against the pawl 122 to hold the hook 124 in the position of interference with the movement of flange 62.

However, in addition, there is provided a manually controllable button 136, which is slidable upwardly and downwardly in the casing 10, in a slot provided for that purpose. The function of the button 136 is to engage the extremity 138 of the pawl 122 to pivot the pawl about the pin 120 and to displace the pawl against the pressure of leaf spring 130 so that the hook 124 is displaced to a position which is outside of any position of interference with the upward movement of flange 62. For this purpose, the push button 136 is provided with a cam surface 137 which engages against extremity 138.

Thus, it will be seen that a convenient manual control is provided whereby selective operation is possible with the pipette of the invention and whereby there is thus provided, on one hand, a repetitive type of operation in which a carefully metered amount of fluid is repeatedly dispensed and, on the other hand, a one-shot type of operation after which there is enabled an operation of adjustable stop 92 to change the amount of fluid to be next metered.

From what has been stated above, it will now appear that the invention provides a pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means and a dispensingoperation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of like amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit the adjusting of the volume between dispensing operations.

The pawl 122 mentioned hereinabove is adapted to engage the flange or projection on the sheath constituting the push button 22 and is intended to hold the piston in fully depressed position whereby a facile selection is available for the next sequential dispensing operation. However, the position of the pawl can readily be altered so as to hold the piston in a position intermediate fully depressed position and fully released position.

The above apparatus finds important usage in clinical and biochemical laboratories. It may be made with different capacities, such as, for example, 2, and ml.

With respect to its operation effectiveness, the following table gives evidence of the improvement achieved by use of the invention:

Size 2 ml 5 ml l5 ml Range .01 to 2 ml .1 to 5 ml .2 to l5 ml Accuracy: ML i .0005 .t .0l 2 .02 :t .25 i .2 .l4 Reproducibility (Standard Deviation): ML 1 .0025 t .003 I .0035 1 .l25 .06 i .024

in FIG. 5, the illustrated valve possesses a number of features. Being of Teflon or the like, not only is the illustrative valve inert to the vast majority of fluids which might be processed, but further its shape is such as to be deformable at certain critical points to make it openable at relatively low pressures.

Reference is made particularly to undercut 148 forming a skirt 150. This skirt is readily spread at low pressures to form an excellent seal with encircling portion 152 of outer member 154. Moreover, the skirt has a slightly smaller inner diameter (e.g., on a bias from 0.327 to 0.330 inches) than the outer diameter of the skirt (e.g., also on a bias from 0.331 to 0.334) to permit of a press fit. At the same time, the inner diameter of the skirt is such (e.g., about 0.290 inches) as to make the skirt thin and thus deformable under low pressures.

Further, the angle of surface 156 with'respect to the vertical is about 35 with the seat wall tapering off to about 0.015 inches at its upper extremity to yield to the pressure of ball at the upper extremities of the scat.

What is claimed is:

l. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, 'a" casing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed means to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, said piston means including a rod and a piston on said rod, a hub in said tube slidably supporting said rod, said hub being cup shaped, and a cup shaped stopper on said rod and a spring between said hub and stopper, said spring cooperating with said stopper to form a dashpot to minimize the application of shock to the fluid.

2. A pipette as claimed in claim 1 comprising a spring acting on said sheath to urge the same to partly withdrawn position relative to said tube. p

3. A pipette as claimed in claim 2 wherein said adjusting means includes an adjustable stop having a position of interference relative to said sheath.

4. A pipette as claimed in claim 3 wherein said sheath includes a projection to engage said stop.

5. A pipette as claimed in claim 4 wherein said projection is a flange at least partly encircling said sheath.

6. A pipette as claimed in claim 1 comprising means on said fixed means to form a hydraulic seal with said tube.

7. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, a casing into which said plunger means is de pressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed means to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, a spring acting on said sheath to urge the same to partly withdrawn position relative to said tube, said adjusting means including an adjustable stop having a position of interference relative to said sheath, said sheath including a projection to engage said stop, said further means including a pawl adapted to engage said projection to hold the piston means in fully depressed position.

8. A pipette as claimed in claim 7 comprising means pivotally mounting said pawl on said casing, a leaf spring engaging said pawl and moving the same to a position to engage said projection, and a manually operable button to pivot the pawl against the leaf spring to release the projection, said button being effective to keep the pawl removed from said projection.

9. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, a easing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed means to limit the extent to which the plunger means can be depressed relative to said tube,

said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, a spring acting on said sheath to urge the same to partly withdrawn position relative to said tube, said adjusting means including an adjustable stop having a position of interference relative to said sheath, said adjustment means including a threaded rod on which said stop is threadably engaged.

10. A pipette as claimed in claim 9 comprising an index on said stop and a scale on said casing cooperating with said index to show the selected amount of fluid to be drawn in.

11. A pipette as claimed in claim 9 comprising tie rods parallel to said threaded rod and passing through said stop to prevent the latter from cocking.

12. A pipette as claimed in claim 9 comprising a knob on said threaded rod to rotate the latter to adjust said stop, said casing being provided with an opening exposing said knob.

13. A pipette as claimed in claim 9 wherein said stop encircles said sheath.

14. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, a easing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed mean to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, said piston means including a rod and a piston on said rod, a hub in said tube slidably supporting said rod, said hub being cup shaped, and a cup shaped stopper on said rod and a spring between said hub and stopper.

15. A pipette as claimed in claim 14 wherein said intake and dispensing means each include one-way ball valves.

outer member, pyrex glass ball and seating mcans for said ball including relatively thin skirt adapted for deforming under relatively low pressures to form a seal with said outer member.

19. A pipette as claimed in claim 18 wherein said seat includes a tapered, relatively thin-walled seat for said ball. 

1. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, a casing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed means to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intakE and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, said piston means including a rod and a piston on said rod, a hub in said tube slidably supporting said rod, said hub being cup shaped, and a cup shaped stopper on said rod and a spring between said hub and stopper, said spring cooperating with said stopper to form a dashpot to minimize the application of shock to the fluid.
 2. A pipette as claimed in claim 1 comprising a spring acting on said sheath to urge the same to partly withdrawn position relative to said tube.
 3. A pipette as claimed in claim 2 wherein said adjusting means includes an adjustable stop having a position of interference relative to said sheath.
 4. A pipette as claimed in claim 3 wherein said sheath includes a projection to engage said stop.
 5. A pipette as claimed in claim 4 wherein said projection is a flange at least partly encircling said sheath.
 6. A pipette as claimed in claim 1 comprising means on said fixed means to form a hydraulic seal with said tube.
 7. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, a casing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed means to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, a spring acting on said sheath to urge the same to partly withdrawn position relative to said tube, said adjusting means including an adjustable stop having a position of interference relative to said sheath, said sheath including a projection to engage said stop, said further means including a pawl adapted to engage said projection to hold the piston means in fully depressed position.
 8. A pipette as claimed in claim 7 comprising means pivotally mounting said pawl on said casing, a leaf spring engaging said pawl and moving the same to a position to engage said projection, and a manually operable button to pivot the pawl against the leaf spring to release the projection, said button being effective to keep the pawl removed from said projection.
 9. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the neXt sequential dispensing operation, a casing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed means to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, a spring acting on said sheath to urge the same to partly withdrawn position relative to said tube, said adjusting means including an adjustable stop having a position of interference relative to said sheath, said adjustment means including a threaded rod on which said stop is threadably engaged.
 10. A pipette as claimed in claim 9 comprising an index on said stop and a scale on said casing cooperating with said index to show the selected amount of fluid to be drawn in.
 11. A pipette as claimed in claim 9 comprising tie rods parallel to said threaded rod and passing through said stop to prevent the latter from cocking.
 12. A pipette as claimed in claim 9 comprising a knob on said threaded rod to rotate the latter to adjust said stop, said casing being provided with an opening exposing said knob.
 13. A pipette as claimed in claim 9 wherein said stop encircles said sheath.
 14. A pipette comprising fluid intake means, fluid dispensing means, control means to draw fluid in via said intake means and eject the drawn in fluid via the fluid dispensing means in a dispensing operation, adjusting means effective with said control means to adjust the amount of fluid drawn in, said control means being normally effective for repetitive dispensing of the amounts of fluid as selected by said adjusting means, and further means operatively associated with said control means and manually operable to limit the operation of the control means to a single dispensing operation to permit adjusting the volume between dispensing operations, said control means including plunger means depressible for ejecting drawn in fluid for a given dispensing operation and releasable to draw in a selected amount of fluid for the next sequential dispensing operation, a casing into which said plunger means is depressible, a tube in said casing to receive said plunger means, support means to support the tube in said casing, and fixed mean to limit the extent to which the plunger means can be depressed relative to said tube, said tube being coupled with said intake and dispensing means, said plunger means including a sheath encircling said tube and displaceable thereon and piston means in said tube displaceable by said sheath, said piston means including a rod and a piston on said rod, a hub in said tube slidably supporting said rod, said hub being cup shaped, and a cup shaped stopper on said rod and a spring between said hub and stopper.
 15. A pipette as claimed in claim 14 wherein said intake and dispensing means each include one-way ball valves.
 16. A pipette as claimed in claim 14 wherein said intake means has an external shape adapted to be accommodated in an opening in a reservoir.
 17. A pipette as claimed in claim 16 comprising a filter and a flexible tube coupling the filter to the intake means.
 18. A pipette as claimed in claim 15 wherein each said valve includes an outer member and, within said outer member, pyrex glass ball and seating means for said ball including relatively thin skirt adapted for deforming under relatively low pressures to form a seal with said outer member.
 19. A pipette as claimed in claim 18 wherein said seat includes a tapered, relatively thin-walled seat for said ball. 